This invention relates, in general, to insulated gate transistors (IGT), and more particularly, to an insulated gate transistor having a high reverse breakdown voltage.
Insulated gate transistors, also known as insulated gate bipolar transistors (IGBT), are well known. The basic IGT suffers from a latch-up condition. The latch-up condition was alleviated by the addition of a highly doped N layer positioned between the anode and the epitaxial layer of the IGT transistor. This highly doped N layer, also called a buffer layer, is shown in U.S. Pat. No. 4,364,073 which issued in 1982 to Becke et al. This U.S. Pat. No. (4,364,073) is hereby incorporated herein by reference. One of the disadvantages of adding the highly doped N layer to the basic IGT transistor is that the reverse breakdown voltage of the device decreased. The highest achievable reverse breakdown voltage was approximately 25 volts. Although these IGTs, having reduced latch-up and reverse blocking voltage, are useful in many applications, there are applications where it would be desirable to have an IGT with a high reverse blocking voltage.
Accordingly, it is an object of the present invention to provide an insulated gate transistor having high reverse breakdown voltage capability.
Another object of the present invention is to provide an insulated gate transistor having high breakdown voltages in both forward and reverse directions, as well as being resistant to latch-up conditions.
Another object of the present invention is to provide an improved insulated gate transistor being capable of withstanding high reverse voltages and yet is easily manufactured.
A further object of the present invention is to provide an insulated gate transistor having a high reverse breakdown voltage and yet maintaining a fast turn-off speed.